Various types of conventional integrated circuit (IC) sockets for attaching IC packages are known. Each of the IC packages has a large number of contacts that are arranged in a matrix-like array. The IC packages may be classified as pin grid array (PGA) packages, ball grid array (BGA) packages, or land grid array (LGA) packages depending on the shape of an electric contact portion of the contacts. The contacts in each of the IC packages are brought into contact with corresponding contacts arranged in a housing of the socket to establish electrical connections therebetween. The mating of the contacts in the IC package with the corresponding contacts in the socket typically causes a large contact pressure to be exerted on the socket by the loading mechanism loading force. Various socket configurations are known to provide the socket with sufficient strength to prevent deformation of the same.
FIG. 1 shows a cross-sectional of a portion of a prior art LGA socket 100 mounted onto a PCB 101 by way of an array 103 of solder balls. Hereinafter, a “portion” of the socket will be referred to as “socket,” it being understood that only a portion of the socket being described has been shown. A LGA package 102 is shown as having a package substrate 116 and being mounted onto the PCB 101 by way of the socket 100 by being fixed and seated within the socket. The socket 100 includes a housing 104 having a solder ball standoff element 106 and a package seating plane standoff element 108 at a side thereof. The socket 100 further includes conductive through-portions 113 extending therethrough to outer contacts 112 on the PCB side thereof. The socket 100 further includes on its package side inner flexible contacts 114 contacting corresponding LGA lands. The combination of through-portions 113, outer contacts 112 and inner contacts 114 make up the socket through-contacts 115 as shown. A vertical load VL is shown acting onto a loading point of the package substrate. Reaction forces RF act on each of the solder ball standoff element 106 and seating plane standoff element 108 to counterbalance the VL. High risk areas of the socket 100 and package 102 for material yielding are indicated in FIG. 1 by way of star-shaped indicators.
To prevent deformation of a housing of a LGA socket when a large force is exerted in a vertical direction, such as VL shown in FIG. 1, a pair of metal reinforcements may be provided according to one prior art solution. The metal reinforcements clamp the LGA package and the socket fitted with the LGA package together from opposite sides (from both front and back surface sides) of a printed circuit board to which the socket is fitted. The metal reinforcements may include a loading plate or heat sink disposed on the LGA package and a board restraint plate disposed under a mount board. A screw may be passed through the loading plate or heat sink and the board restraint plate at each corner thereof and may be tightened by a nut to prevent deformation of the socket. The printed circuit board has apertures on a periphery thereof for accommodating the screws. This configuration, however, requires a larger footprint on the printed circuit board than that actually occupied by the socket itself. Thus, the socket size is large, a large number of parts, such as, screws, are required, and assembly is complicated.
According to another prior art solution, the LGA package and the socket may be disposed between a heat sink and a printed circuit board, and the socket is directly screwed to the printed circuit board. In this configuration, however, the printed circuit board is susceptible to warping.
Additionally, according to yet another prior art solution, a lever may be used to connect and maintain electrical connections between contacts of an IC package and corresponding contacts of a socket. The lever may be adapted to be engaged with a protrusion or elastic interlocking element integrally formed with a resin housing of the socket. The lever may be locked by the protrusion or elastic interlocking element to hold the electrical connections between the contacts. Since the protrusion or the elastic interlocking element is made of resin, the protrusion or the elastic interlocking element is apt to wear out due to friction with the lever during operation of the lever. The socket, therefore, is not durable. Forming the protrusion or the interlocking element as a separate metal member, on the other hand, increases the number of parts and the manufacturing costs.
Further, if the housing of the socket deforms when the LGA package is pressed by a cover member to form electrical connections between the contacts, the electrical contact array may become warped and deteriorate the electrical connections between the contacts. A force applied to the lever for actuation will also not efficiently be transferred.
Related prior art solutions for strengthening a LGA socket may include (1) increasing the stiffness of the package by increasing the IHS step thickness, (2) increasing package stiffness, (3) increasing the socket housing thickness, or (4) adding a metal frame onto the socket. However, the first three solutions go against market needs to minimize package and/or socket size, and the fourth solution adds significant cost to the package.
For simplicity and clarity of illustration, elements in the drawings have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Where considered appropriate, reference numerals have been repeated among the drawings to indicate corresponding or analogous elements.